Biodistribution of Radiolabeled Monoclonal Antibody E48 Igg and F(Ab')2 in Patients with Head and Neck Cancer

Biodistribution and pharmacokinetics of radiolabeled mAb E48 IgG and E48 F(ab')2 were analyzed and compared in 39 patients with histologically proven squamous cell carcinoma of the head and neck who were included in a radioimmunoscintigraphy study and underwent surgery 44 h after injection. Three groups of patients were distinguished: group 1 {n = 19) received technetium-99m (99mTc)-labeled E48 F(ab')2, group 2 (n = 9) received99mTc-Iabeled E48 IgG, and group 3 (n = 11) received99mTc- and131I-labeled E48 IgG as well as125I-labeled F(ab')2. Two patients in group 1 and four patients in group 3 received a high mAb dose (10-50 mg), while all other patients received a low mAb dose (1-4 mg). From all patients in groups 2 and 3 biopsies from the surgical specimen were obtained 44 h postinjection. Tumor uptake of99mTc-labeled E48 IgG was high, ranging from 0.007 to 0.082% of the injected dose/g, with a mean of 0.031 ± 0.020% of the injected dose/g. The mean tumor: nontumor ratio of this conjugate was 2.8 for mucosa, 4.6 for bone marrow aspirate, 4.1 for blood, 20.3 for fat, and 21.0 for muscle. Activity uptake in tumor positive lymph nodes was 4.7 times higher as compared to negative lymph nodes. Sixteen h postinjection radioimmunoscintigraphy revealed activity uptake in the primary tumor, lymph node metastases, oral cavity, and adrenal glands. Using regions of interest, the uptake in the adrenal glands was estimated to be 0.050% of the injected dose/g. If a high mAb dose was used, no adrenal glands were visualized and the uptake in the oral cavity was clearly diminished, while the tumor uptake and tumor:nontumor ratios were increased. The mean elimination half-lifes tx1/2 α and t1/2 β in plasma were: for E48 IgG (n = 20) 6.6 ± 2.6 and 54.1 ± 24.3 h and for E48 F(ab')2 (n = 19) 2.3 ± 0.4 and 19.9 ± 4.6 h, respectively. Tumor uptake of131I-labeled E48 IgG was 49% higher than of I25I-labeled F(ab')2. For most tissues except normal oral mucosa, tumor:nontumor ratios were slightly higher for F(ab')2 than for IgG. The present study shows that mAb E48 accumulates selectively and to a high level in head and neck squamous cell carcinoma. Although no definite conclusions can be drawn as to which mAb form is more suitable, IgG or F(ab')2, mAb E48 seems to have potential for radioimmunotherapy in head and neck squamous cell carcinoma patients.